Sintered carbide compositions



1956 G. w. LUCAS ET AL SINTERED CARBIDE COMPOSITIONS Filed May 13, 1954 ZOOX Inventcrs: George W. Lucas, Carl -S.W'

leciman,

Their Att'cawney.

United States 2,731,110 SINTERED CARBIDE- COMPOSITIONS; Gejorge W.Lucas, St. Clair Shores, and Garl S. Wiednian,

Oakland; Mich., ,assignors to General Electric Company, a corporation of New Yul-k Application May 13, 1954, Serial No. 429,446 5 clams. or. 29 -182.?) a

This invention relates is hard metal ce apesitiess and more particularly to improvements in such compositions commercially known as cemented multi-carbides which are composed essentially of tungsten carbide; with a se ondary carbide such as titanium carbide. tantalum carbide, 'z'ir'coni'urn carbide, sf oli'iinbiiirn carbide, and a metallic binder selected from the greup consisting of iron, cobalt and nickel or thereof. More speeifi'cally, this invention relates to hard metal compositions of the foregoing type which are eminently siiitable for inachining and cutting of steel and ferrous alloys:

Compositions presently employed in making cutting tools and the like are typified by fine grain size of the tungsten carbide crystal component together with the use of an auxiliary metal binder. The compositions presently manufactured contain tpngsten carbide crystals meastiring predominantly the range of 0.5 to T inierons. A usual range is from 3 to 8 miei'ons. Generally, the amount of binder "metal employed in conventional multi= carbides ranges up to about 12% by weight of the composition; the low binder range being employed for maximum wear resistance while the high binder range being used for Patent 0 7' providing maximum toughness and resulting shoclg resistance. It is, however, currently considered to be impractical to utilize less than about by weight of binder since breaking, chipping or spalling of the to'ol's generally results. In these applications slight mo'difieati'onsin fearbide grain size have been resorted to in an eifo'rt to overcome brittleness. Moreover, a secondary carbide such as titanium, tantalum, zirconium or columbium carbide is usually employed in steel cutting compositions of this type to provide resistance in the multi-carbide composition to cratering caused by welding and erosion from the material being machined or cut.

The multi-carbides which to date. ha mercial value in this category are cha 12 I a large portion of the tungsten carbid and all or In t of the secondary carbide, such as, for example, tita urn carbide, in the form of a solid solution. Beneficial results realized in the use of such compositions have been attributed to the existence of a solid solution carbide the sintered product. In fact, prior workers have 'sti'ess'ed the importance of promoting the formation of a solid solution to as complete a degree as possible fwi any given composition. Additionally, materials which contain *a secondary carbide, such as titaniumcai bide, in addition to tungsten carbide and auxiliary bin er areal have been consistently described in the literature and rs and patents as requiring the maximum of tungsten carbide to be in solution in the secondary carbidefor best performance.

i ;In preparing conventional multi-carbide compositions,

it l1 as also been considered that a grain size in the range of from 1 to 10 microns is the most useful. In present practice, grain sizes as large as 25 microns would be considered extremely rare and the average for most presently made materials is about 3 microns.

For the first time, the present invention provides cemented multi-carbide compositions which inherently are possessed of a higher degree of toughnessand wear resistance than present conceptsvvould lead those skilled in the art to expect, and is based on new concepts which completely refute those previously accepted both with re? gard to crystal size and solid solution.

The magnitude of ditference in the size of tungsten carbide crystals employed in the present invention as compared to conventional multi-carbide compositions is best illustrated by reference to the accompanying drawings er 4 Figs. -1 2 arephotomicrographs showing magnifications at 1 500 and 200 diameters respectively of a multicarbide composition of the invention, and

Figs. 3 and 4 are photomicrographs showing magnifications at 1 500 and 200 diameters respectively of a multicarbide composition having conventional grain size tungsten carbide crystals.

In all figures the large angular crystals are tungsten carbide.

In accordance with the present invention, it has been found that thepresence of extremely largegrains of tungsten carbide in sintered multi-carbide compositions is highly desirable and provides a sintered cemented multicarbide composition of maximum wear resistance and toughness. Thus, inulti-carbide compositions having tungsten carbide crystals as large as 250 microns in some cases and with a comparatively large number of the tungsten arbid e grains in the 25 to micron category have been found eminently superior to corresponding conventional compositions. It will be noted that this range is considerably higherthan the range of grain size heretofore considered or used, being larger in the order of ten times or more. t v A The copending application of George W. Lucas Serial No. 429,445 filed concurrently herewith and assigned to the assignee of the present invention is directed to and claims therein the largegrain size tungsten carbide compositions .per se (as distinguished from the multi-carbide compositions of the present application.) which. exhibit a high degree of toughness and. resulting shock resistance coupled with excellent wear resistance. The term, macro-crystalline tungsten carbide, as herein used is intended to define large grains or crystals of tungsten carbide having grain sizes of the order of '25 to 250 microns. I

A second, entirely new concept of the present invention lies in the use of macro-crystalline tungsten carbide for the purpose of inhibitingor retarding the formation er solid -solution carbides. This is also directly contrary to present concepts which attribute "c r'ta'in ad antagesio solid solutions. It has been found that by inhibiting "the formation of solid solution carbides, higher -piereenta ges Patented Jan. 24, 1 956 of secondary carbides,- for example, titanium carbide, can be used in place of. a portion of the tungsten carbide. Moreover, the use of higher percentages of a secondary carbide, such as titanium carbide, can be resorted to without appreciably decreasing toughness, if tungsten carbide grain sizes in the range herein described are employed and the formation of solid solution carbide is inhibited. In fact, toughness is further improved by using coarser grained tungsten carbide. The use of such coarser grained carbide results in a consolidation of the binder. The net result is a product of improved toughness.

Another substantial advantage accruing from the herein described use of macro-crystalline tungsten carbide is the reduction in the percentages of binder metal required as compared to most present commercial grades of multicarbides. For example, the percentages of binder metal presently used in commercial steel cutting cemented multi-carbide grades are in the order of 5% to 12%, by weight, as contrasted to the range of binder metal employed in producing the compositions of the present invention, specifically from about 1.5 to by weight. The major advantage in the binder reduction is that more hard carbide, which is essentially responsible for the elfectiveness of the cutting tool, and does the actual work of cutting, can be employed in the compositions.

The coarse grained tungsten carbide compositions herein described may be manufactured by processes presently employed for the manufacture of conventional multi-carbides with some modifications. One important modification in producing the compositions is in the use of a double ball milling cycle in which the first milling includes the secondary carbide and the binder. metal. In this first milling, there may also be present a portion of the tungsten carbide. The second milling is for a relatively short period of time and includes the addition of only the coarse tungsten carbide. By this method excessive attrition of the coarser grains is prevented.

In the preparation of the multi-carbide compositions of the invention varying percentages of tungsten carbide may be employed. Generally, a range of tungsten carbide of from about 60 to'about 90%, by weight of the composition, may be utilized to advantage.

Secondary carbides suitable for preparing the present compositions include titanium, tantalum, zirconium and columbium carbides. The proportions of secondary carbide can vary widely, for example, from about 5 to about by weight of the final composition. The grain size of the secondary carbides employed lies in the conventional range of 0.5 to 10 microns.

The binder metals found suitable in preparing the compositions of the'invention include cobalt, nickel, and iron in percentages varying from about 1.5 to about 10%, by weight, 'of the final composition. Of these, cobalt is the-preferred binder. However, nickel or iron may be used instead of or admixed with cobalt. Thus, nickel may be used in place of all or part of the cobalt, or about one-half of the nickel or cobalt may be replaced with iron. When mixtures are employed, the combined weights of the metals should preferably be in approximately the same percentage range.

While tungsten carbide crystals as large as 250 microns may be used to advantage in preparing compositions of the 'pre'sentinvention, the tungsten carbide component of the sintered material may be predominantly (50% or overby weight or volume of the tungsten carbide) in the 25 to 150 micron range. However, it will be understood that occasional grains on' either side of this range may be present in the composition.

In order that those skilled in the art may more fully understand how the present invention is carried into efiect, the following specific examples of compositions employed .in' fabricating cutting tools were prepared. The tungsten carbide grains employed in the compositions were of the order of 25 to 250 microns with a size are expressed both by weight and by volume.

Percentage Percentage by Weight by Volume Example 1:

Tungsten carbide 74. 3 50. 0 Titanium carbide. 21. 4 45. 0 Col) 4.. 3 6. 0 Example 2.

Tungsten carbide. 64. 3 45. 0 Titanium carbide- 18. 3 40. 0 Tantalum carbide 13. 3 10.0 Cobalt 4. 1 5. 0 Example 3:

Tungsten carbide 65. 4 40. 0 Titanium carbide. 27. 6 52. 5 Cobalt 3. 5 3. Nickel 3. 5 3. 75 Example 4:

Tungsten carbide 63.0 43. 8 Titanium carbide 18. 0 39. 0 Tantalum carbide 12. 9 9. 7 Cobalt 6.1 7. 5 Example 5:

Tungsten carbide 61. 5 42. 5 Titanium carbide.. 17. 6 38. 0 Tantalum carbide" 12. 7 9. 5 Cob 8. 2 10.0 Example 6 Tungsten carbide- 68. 1 50. 0 Titanium carbide- 14. 0 32. 0 Tantalum carbide.. 10. 1 8.0 Cobalt 7. 8 10.0 Example 7:

Tungsten carbide 69. 1 40. 0 Titanium carbide. 18. 8 40. 0 Tantalum carbide-.. 13. 7 10. 0 Cobalt 8. 4 10. 0

Cutting tools were made from representative compositions of the foregoing examples, and compared with tools made of presently commercially available grades of Carboloy cemented multi-carbides, namely, Grades 78, 78B, 78C and 370 now made and sold by the General Electric Company and all having cenventional fine grain tungsten carbide. Accelerated cutting tests were performed on a steel log approximately 10 in diameter, using the following cutting conditions:

Surface, ft./min 800 Depth of cut ..inch Feed/revolution do .022

7 Under these conditions of testing the following total tool life was obtained:

* In this case the test was discontinued before failure.

From the foregoing results, it can be readily discerned that the multi-carbide compositions of the present invention present a notable advance. As shown above, tools made of compositions of the present invention had much longer total life than conventional tools.

Materials having the'same compositions as those of the foregoing examples were prepared with conventional fine tungsten carbide grains, and tools made of these materials failed due to breakage under conditions of the above test because they were high in hardness and wear resistance but lacking in toughness.

While the invention has been described and claimed and particularly illustrated with reference to the production of cutting tools, it will be obvious to those skilled in the art that the invention is of wide application in the cemented carbide field. Obvious additional uses for the compositions disclosed will readily suggest themselves and include use in steel machining operations such as turning, milling, boring, broaching, shaping, etc.

What we claim as new and desire to secure by Letters Patent of the United 'States is:

1. A sintered, hard metal composition consisting essentially of from about 60 to about 90%, by weight of the sintered product, of macro-crystalline tungsten carbide in which more than 50% of the crystals are larger than 25 microns, from about to about 30%, by weight of the sintered product, of at least one additional carbide selected from the group consisting of titanium carbide, tantalum carbide, zirconium carbide and columbium carbide, and about 1.5 to about by weight of the sintered product, of a binder metal for said carbides se' lected from the group consisting of cobalt, nickel, iron and mixtures thereof.

2. A sintered, hard metal composition consisting essentially of from about 60 to about 90%, by weight of the sintered product, of tungsten carbide crystals ranging in size from 25 to 250 microns, a major portion of said tungsten carbide crystals having a predominant grain size in the range of from 25 to 150 microns, about 5 to about 30%, by Weight of the sintered product, of an additional carbide selected from the group consisting of titanium carbide, tantalum carbide, zirconium carbide and columbium carbide, and about 1.5 to about 10%, by weight of the sintered product, of a binder metal selected from the group consisting of cobalt, nickel, iron and mixtures thereof.

3. A sintered, hard metal composition consisting essentially of from about 60 to about 90%, by weight of the sintered product, of tungsten carbide crystals ranging in size from 25 to 150 microns, about 5 to about 30%, by weight of the sintered product, of an additional carbide selected from the group consisting of titanium carbide, tantalum carbide, zirconium carbide and columbium carbide, and about 1.5 to about 10%, by weight of the sintered product, of cobalt.

4. A sintered, hard metal composition consisting essentially of from about to about by weight of the sintered product, of tungsten carbide crystals having a predominant grain size in the range of from 25 to microns, about 5 to about 30%, by weight of the sintered product, of an additional carbide selected from the group consisting of titanium carbide, tantalum carbide, zirconium carbide, and columbium carbide, and from about 1.5 to about 10% by Weight of the sintered product, of cobalt.

5. A hard metal, multi-carbide cutting tool material consisting essentially of from about 60 to about 90%, by weight of the tool material, of macro-crystalline tungsten carbide in which more than 50% of the crystals are larger than 25 microns, about 5 to about 30%, by weight of the tool material, of at least one additional carbide selected from the group consisting of titanium carbide, tantalum carbide, zirconium carbide and colornbium carbide, and about 1.5 to about 10%, by weight of the tool material, of a binder metal selected from the group consisting of cobalt, nickel, iron and mixtures thereof.

References Cited in the file of this patent Goetzel: Treatise on Powder Metallurgy," pages 108-119, published 1950.

vol. II, 

1. A SINTERED, HARD METAL COMPOSITION CONSISTING ESSENTIALLY OF FROM ABOUT 60 TO ABOUT 90%, BY WEIGHT OF THE SINTERED PRODUCT, OF MACRO-CRYSTALLINE TUNGSTEN CARBIDE IN WHICH MORE THAN 50% OF THE CRYSTALS ARE LARGER THAN 25 MICRONS, FROM ABOUT 5 TO ABOUT 30%, BY WEIGHT OF THE SINTERED PRODUCT, OF AT LEAST ONE ADDITIONAL CARBIDE SELECTED FROM THE GROUP CONSISTING OF TITANIUM CARBIDE, TANTALUM CARBIDE, ZIRCONIUM CARBIDE AND COLUMBIUM CARBIDE, AND ABOUT 1.5 TO ABOUT 10%, BY WEIGHT OF THE SINTERED PRODUCT, OF A BINDER METAL FOR SAID CARBIDES SELECTED FROM THE GROUP CONSISTING OF COBALT, NICKEL, IRON AND MIXTURES THEREOF. 